Disks for use in computer memory storage devices have been manufactured for some years by utilizing a process for sputtering magnetic media on various diameters and thicknesses of aluminum, glass and ceramic disks. As part of the developmental process, groups of disks have been held in a holder/carrier to permit magnetic material to be simultaneously sputtered on the opposed planar surfaces of each disk without any cross-contamination of magnetic material from one side of the disk(s) to the other side of the disk(s). U.S. Pat. No. 4,595,481 issued to the Assignee of this application describes such a carrier where chamfered edges of the disk are supported by a V-groove arc at a bottom of a plate bore through the carrier plate and rests on an arc edge of an upper recess formed above the plate bore. The carrier of U.S. Pat. No. 4,589,369 has a similar upper ridge but includes a square U-shaped groove at the bottom of the bore into which a relatively wide outer annulus of the disk interfits, including a part of the planar disk surface. U.S. Pat. No. 4,634,512 shows and claims an improvement to the -481 patent where two-part plug portions preferably with magnetic surfaces and grasp knobs are employed to close the central aperture of the disks. The central aperture in disk use is utilized to mount the finished disks on a computer disk drive spindle. The plug also aids in robotically mounting the disk(s) in the carrier, to remove the disks from the carrier and to move the disk blanks and finished disks from and to a suitable shipping or storage cassette. U.S. Pat. No. 4,735,701 describes a one-piece plug for closing the disk central aperture.
It has become more important to store more and more data on a disk and to decrease the space between data tracks on the operating planar surfaces of a disk. Such spaces are typically in the range of 0.010 inch to 0.080 inch (0.25 mm to 2.03 mm) so as to prevent cross-talk between the tracks. Likewise, it has been determined that one should try to maximize the usability and thus storage capacity at the outer diameter of each disk. Since a read-write head of a typical disk drive reads signal amplitude, that signal tends to drop off at the outside diameter (O.D.) of the disk at the outer track(s) due to the absence of a normal magnetic layer at that disk O.D. The signal strength is normally a function of the disk radius. For example, disk manufacturers are ask to guarantee data recovery out to about 1.80 inches (45.7 mm) from the disk center in a 51/4 inch (130 mm) disk. In typical present day disks of that size, the disk signal actually "decreases" at about 1.81 inch (46.0 mm) from the disk center. Since data storage is at a circular maximum at the disk O.D. even the addition of 0.05 inches (1.25 mm) of added O.D. band width which will support usable magnetic media would appreciably increase the data storage capacity of the disk. Comparable improvements would be possible with 48 mm, 65 mm and 95 mm and other sizes of magnetic storage disks.
FIGS. 11 and 12 are graphs of tests on the front and back respectively of a prior art disk which had been held during manufacture in a carrier of the type disclosed in U.S. Pat. No. 4,595,481. The abscissa denotes the reading at 90.degree. positions around the disk while the ordinate denotes the coercivity of the magnetic layer in oersteds. Various plots were made at 1" (25.4 mm), 1.25" (31.8 mm), 1.50" (38.1 mm), 1.75" (44.5 mm) and 1.85" (47 mm) radial portions from the disk center. It is to be noted that in the lower plot at a radial distance of 1.85" the coercivity drops perceptibly from an average value of about 1580 Oe to a low at the 180.degree. position of about 1520 Oe. On the back side of the disk drop-offs of an average coercivity of about 35 Oe are seen at the 270.degree. position. These are to be compared with FIGS. 13 and 14 showing results on disks made with the apparatus and method of the present invention where essentially all coercivities are at or above 1600 Oe with the outer 1.85 radius having coercivities of about 1605 Oe on the front and about 1635 Oe on the rear side. Further, microphotos plotting signal amplitude versus disk radius show irregular signals in the prior art disks as the O.D. of the disk planar surfaces is approached unlike the usable signals in the disks manufactured by the method and carrier of the present invention.
FIGS. 15-18 show graphs of amplitude percentage plotted against disk radius from the I.D. for both prior art disks using a prior art carrier (the rectangles) and the disks manufactured by the method and apparatus of the present invention (the triangles). As can be seen the prior art disk drop off in signal amplitude (a measure of the magnetic storage capacity) starts generally at a 1.79" radius length. In the (new) disk manufactured as described hereafter, the amplitude percentage actually raises both on the disk front surface and disk back surface from about the 1.75" (44.5 mm) radius position all the way to the 1.83" (46.5 mm) O.D. of the planar annular band of the disk, to a value of up to 116% amplitude percentage, in both line frequency (FIGS. 15-16) and half line frequency (FIGS. 17-18) tests. The latter tests are considered to be "worst case" tests. From FIGS. 11, 12 and 15-18 it can be seen that the outside 0.05" (1.25 mm) or more of the planar band in the prior art disks is not usable for data storage.
Further, prior art disk carriers have been the cause of generation of contaminants which can attach to or become occluded in the magnetic media coated on the disk. This results in an area which will not properly store the data and subsequent rejection of the disk. Contamination of the disk can come about by the generation of contaminants in the handling or plugging of the disk and in any undesirable contact of the annular bands of the disk with the disk carrier during disk loading, magnetic media coating or disk unloading causing surface scratches to the parallel portions (annular bands) of the disk.
Heretofore conventional wisdom when simultaneously coating both sides of a disk held in a carrier has been to "seal" off plasma directed to one side of the disk from plasma directed to the other side of the disk. First the disk central aperture has been fully plugged and second the entire 360.degree. of the disk periphery has been sealed by a bottom groove and a top lip so that plasma cannot pass between the disk periphery and the carrier opening. Such sealing has tended to cause contacting of surfaces on which the media is to be coated and poor coating of the outer peripheral of the disk plane surfaces.
A problem of disk "drop-out" from the carrier, i.e. the disk falling out of the carrier, due to the various disk handling and carrier handling during sputtering has also occurred. If a disk is not properly held in the carrier it can bounce out or be pushed out by the sputtering or handling forces.
In summary, a need has been perceived to meet or exceed customer disk drive specifications in the amount of disk storage at the disk periphery, allow for more accurate and reliable robot loading capability and to increase the stability of the disk in the carrier during handling and sputtering.